Update BaseInputFilter
If value is required, it must be set in $this->data[].
If the value is set and it should not be empty, it must be invalid, even if not required.
Merge remote-tracking branch 'upstream/master'
BaseInputFilter fixed
Implement better text domain merging support
Merge branch 'hotfix/4053'
Close #4053
* hotfix/4053:
  Implement better text domain merging support
Fix loading of a text domain from different sources
Merge branch 'hotfix/4085'

Close #4085
Close #4045
Merge remote-tracking branch 'upstream/master'
Merge pull request #3983 from ossinkine/master

Update BaseInputFilter
Merge branch 'hotfix/3983'

Close #3983
Merge branch 'master' of git://github.com/zendframework/zf2